The present invention regards an external packer for a pipe string in a well, e.g. a completion string, a production string or an injection string. The pipe string consists of several lengths of pipe joined successively as the string is run into the well. The invention also concerns a method of leading at least one line along the pipe string and seamlessly past one or more packers of the present type.
Said line may be e.g. a hydraulic line, a fibre-optic line or another electroconductive line for transmission of actuating power or control signals to downhole well equipment. The line may also be used to transmit measurement signals from downhole measuring apparatus. Moreover, the line may be an injection line used e.g. to pump well treatment fluid into the well. The line is hereinafter simply termed a control line.
The invention is suited for use in petroleum wells, but may equally well be used in other types of wells.
Normally, at least one packer is set around and along at least one pipe string in the well. This is done among other things to separate different well zones in terms of pressure, and also to safeguard the well against outflow of well fluids or reservoir fluids. In this connection it may be necessary to lead one or more control lines of the types mentioned axially past each well packer, so that the line(s) may reach the correct location in the well. This is particularly relevant during well completion. When a control line is passed axially through and past a well packer, it is important to ensure that the guide passage(s) through the packer is/are pressure tight. By doing so, no subsequent leakage can occur between the adjacent zones separated by the packer.
According to prior art, a control line may be led past a well packer via an axial passage through the inner metal core of the well packer, the core being enclosed by an outer sealing element made from a flexible material, e.g. an elastomer. Moreover, the well packer may be provided with several axial passages for lead-through of several control-lines. The two axially opposite openings of a passage are each fitted with a coupling adapted to the type of control line in question. Thus the coupling may be a pipe coupling for a fluid-carrying pipe, or it may be a connector for an electroconductive cable. In the latter case the two connectors of the well packer may be interconnected via a suitable line located in said packer passage. Consequently, each axial side of the packer is connected to a separate length of line.
Thus the control line consists of several successive lengths of line interconnected via said couplings in each well packer. The connections are carried out at the same time as the successive assembly of the associated pipe string takes place, all while this is being lowered into a well. Continuous connection of such lengths of line is demanding and time consuming and therefore also costly. In addition, having several connectors along the control line entails a greater risk of signal deterioration or potential pressure leaks via these. If the control line is electroconductive, several connectors could also lead to a greater risk of inflow of well fluids, which may have an adverse effect on the electrical circuit in the line.
U.S. Pat. No. 6,173,788, on the other hand, shows a well packer with a circular and flexible sealing element which is provided with at least one axial slot in which a control line of the above type may be placed in connection with the assembly of an associated pipe string. With this, a continuous control line may be stretched out past one or more such packers without having to join one or more lengths of line. This also avoids the above disadvantages associated with the use of line connectors. This reduces the installation time for the control line and reduces the risk of pressure leaks from or via the control line, and, if appropriate, will also reduce the risk of well fluid invasion into an electroconductive cable.
The line slot according to U.S. Pat. No. 6,173,788 may be formed in the external surface of the flexible sealing element and face outwards in the radial direction, thereby making it easy to place a control line in the slot. During the subsequent activation and axial compression of the sealing element, the sealing element expands outwards in the radial direction until it makes peripheral contact with an external pipe or borehole wall. On further expansion of the sealing element, the flexible material of the slot wall will in principle be pressed sealingly around the conductor. However, this will require at least one peripheral layer of the sealing element to be formed in a highly pliable and malleable material such as soft rubber, which in the operating position forms a seal around the control line. However, such material properties will reduce the rigidity and shear strength of the sealing element, weakening the ability of the well packer to resist axial compressive forces in the well. When a control line is arranged in the radially outmost surface of the well packer, thus projecting a maximum distance from the pipe string, it also has poor protection against frictional damage caused by possible contact with a enclosing pipe or a borehole during run-in into a well. Similarly, said material in the peripheral layer of the sealing element may also easily sustain damage when running into the well.
The line slot according to U.S. Pat. No. 6,173,788 may also be formed in interfaces between individually adjacent insert components in a flexible sealing element, where, when in the operating position, the components abut each other and form the circular sealing element. Seen in relation to the previous variety, this embodiment is significantly more flexible in use. As an example, the sealing element may be assembled and positioned along the pipe string at short notice, and preferably at a well location. The line slot may also be provided in an axial bore located inside of the external surface of the sealing element, with the control line then being protected against damage when running into the well. It may however be difficult upon activation and expansion of such a discontinuous sealing element, to achieve an adequate pressure seal around the control line and between the adjoining surfaces of the individual insert components.